Jack Kirby (/ˈkɜːrbi/; born Jacob Kurtzberg; August 28, 1917 – February 6, 1994) was an American comic book artist, widely regarded as one of the medium's major innovators and one of its most prolific and influential creators. He grew up in New York City and learned to draw cartoon figures by tracing characters from comic strips and editorial cartoons. He entered the nascent comics industry in the 1930s, drawing various comics features under different pen names, including Jack Curtiss, before settling on Jack Kirby. In 1940, he and writer-editor Joe Simon created the highly successful superhero character Captain America for Timely Comics, predecessor of Marvel Comics. During the 1940s, Kirby regularly teamed with Simon, creating numerous characters for that company and for National Comics Publications, later to become DC Comics.

After serving in the European Theater in World War II, Kirby produced work for DC Comics, Harvey Comics, Hillman Periodicals and other publishers. At Crestwood Publications, he and Simon created the genre of romance comics and later founded their own short-lived comic company, Mainline Publications. Kirby was involved in Timely's 1950s iteration, Atlas Comics, which in the next decade became Marvel. There, in the 1960s, Kirby co-created many of the company's major characters, including Ant-Man, the Avengers, the Black Panther, the Fantastic Four, the Hulk, Iron Man, the Silver Surfer, Thor, and the X-Men, among many others. Kirby's titles garnered high sales and critical acclaim, but in 1970, feeling he had been treated unfairly, largely in the realm of authorship credit and creators' rights, Kirby left the company for rival DC.

At DC, Kirby created his Fourth World saga which spanned several comics titles. While these series proved commercially unsuccessful and were canceled, the Fourth World's New Gods have continued as a significant part of the DC Universe. Kirby returned to Marvel briefly in the mid-to-late 1970s, then ventured into television animation and independent comics. In his later years, Kirby, who has been called "the William Blake of comics", began receiving great recognition in the mainstream press for his career accomplishments, and in 1987 he was one of the three inaugural inductees of the Will Eisner Comic Book Hall of Fame. In 2017, Kirby was posthumously named a Disney Legend for his creations not only in the field of publishing, but also because those creations formed the basis for The Walt Disney Company's financially and critically successful media franchise, the Marvel Cinematic Universe.

Kirby was married to Rosalind Goldstein in 1942. They had four children and remained married until his death from heart failure in 1994, at the age of 76. The Jack Kirby Awards and Jack Kirby Hall of Fame were named in his honor, and he is known as "The King" among comics fans for his many influential contributions to the medium.

Jack Kirby was born Jacob Kurtzberg on August 28, 1917, at 147 Essex Street on the Lower East Side of Manhattan in New York City; he grew up there. His parents, Rose (Bernstein) and Benjamin Kurtzberg, were Austrian-Jewish immigrants, and his father earned a living as a garment factory worker. In his youth, Kirby desired to escape his neighborhood. He liked to draw, and sought out places he could learn more about art. Essentially self-taught, Kirby cited among his influences the comic strip artists Milton Caniff, Hal Foster, and Alex Raymond, as well as such editorial cartoonists as C. H. Sykes, "Ding" Darling, and Rollin Kirby. He was rejected by the Educational Alliance because he drew "too fast with charcoal", according to Kirby. He later found an outlet for his skills by drawing cartoons for the newspaper of the Boys Brotherhood Republic, a "miniature city" on East 3rd Street where street kids ran their own government.

At age 14, Kirby enrolled at the Pratt Institute in Brooklyn, leaving after a week. "I wasn't the kind of student that Pratt was looking for. They wanted people who would work on something forever. I didn't want to work on any project forever. I intended to get things done".

Kirby joined the Lincoln Newspaper Syndicate in 1936, working there on newspaper comic strips and on single-panel advice cartoons such as Your Health Comes First!!! (under the pseudonym Jack Curtiss). He remained until late 1939, when he began working for the theatrical animation company Fleischer Studios as an inbetweener (an artist who fills in the action between major-movement frames) on Popeye cartoons at the same time in 1935. He left the studio before the Fleischer strike in 1937. "I went from Lincoln to Fleischer," he recalled. "From Fleischer I had to get out in a hurry because I couldn't take that kind of thing," describing it as "a factory in a sense, like my father's factory. They were manufacturing pictures."

Around that time, the American comic book industry was booming. Kirby began writing and drawing for the comic book packager Eisner & Iger, one of a handful of firms creating comics on demand for publishers. Through that company, Kirby did what he remembered as his first comic book work, for Wild Boy Magazine. This included such strips as the science fiction adventure "The Diary of Dr. Hayward" (under the pseudonym Curt Davis), the Western crimefighter feature "Wilton of the West" (as Fred Sande), the swashbuckler adventure "The Count of Monte Cristo" (again as Jack Curtiss), and the humor features "Abdul Jones" (as Ted Grey) and "Socko the Seadog" (as Teddy), all variously for Jumbo Comics and other Eisner-Iger clients.